Existing CATV systems employ radio-frequency (RF) links, such as cable and satellite links, or optical links using fiber-optic cables for transmission of TV program material. CATV systems which provide transmissions only from a headend to a plurality of subscribers are called one-way systems. CATV systems which additionally involve transmissions from subscribers' units are called two-way systems.
Some of the one-way systems also employ a telephone link for transmission of management data to the subscribers, while others transmit the management data via the RF or optical links.
Current two-way CATV systems transmit TV and audio programs via cable or satellite and receive data from subscriber units via telephone links. Such systems are hereinafter termed "combination telephone-radio frequency CATV" systems. The data received is mainly CATV subscriber viewing data, subscriber program ratings and the like.
In order to enable telephonic communications, the available CATV converters incorporate modem units which are directly coupled to existing telephone links.
Descriptions of prior art telephonic transponders which are also suitable for CATV systems may be found in several patents. For example, U.S. Pat. No. 3,922,492 to Lumsden describes a remote meter reading transponder which includes a modem. U.S. Pat. No. 3,868,640 to Binnie et al. describes a system for interrogating remote stations via an automatic dialer.
Neither the existing one-way CATV systems nor the two-way systems available today are used to provide services to subscribers. Although existing two-way systems employ telephonic modems, they are mainly used for communication management and for subscriber viewing data readout. Today, telephonic communication via a modem is mostly done at low data rates and for short periods over long intervals, thus leaving the telephonic modems unexploited for long periods.
In an article named "An Evolutionary Approach to the Development of Two-Way Cable Technology Communication" by J.B. Wright, M.P. Block and D.S. McVoy in IEEE Transactions on Cable Television, Vol. CATV-2, No. 1, Jan. 1977, mention is made of proposed two-way CATV systems in which electronic automated newspaper, second class mail and on demand catalogs will be distributed to subscribers.